This invention relates generally to fluid power systems and more particularly to a fluid power assisted steering system for a vehicle.
A prior art fluid power assisted vehicle steering system typically includes a pair of fluid actuated cylinders connected to vehicle wheels, a fluid reservoir, and a pump for pressurizing fluid in the system. An operator responsive control valve is in the system for controlling fluid flow to the cylinders selectively to effect vehicle steering. Fluid flow lines connect the system's components and define one or more continuous fluid circuits.
There have been proposals for systems which will remain operative even though a portion of such system is either damaged and non-functioning or malfunctioning. A problem which these proposals have sought to overcome is rupture of a fluid line with consequent loss of all or substantially all of the pressurized fluid in the system. Such proposals have included independent fluid circuits or isolatable circuit sections. Should damage occur to one circuit or circuit section, that damaged circuit or section is to be isolated from the rest of the system. The remainder of the system is to remain integral and retain as much of the system's fluid as possible. There have been proposals for circuit isolation which take place either manually or automatically.
One proposed power steering system incorporating an automatic cutoff for an independent circuit is disclosed in U.S. Pat. No. 3,865,211 issued to Liebert et al. Liebert et al discloses a two cylinder system where the cylinders are disposed in a series fluid flow relation. When the vehicle is steering, pressurized fluid is directed from the pump to only one of the cylinders and that cylinder powers the vehicle steering.
During normal operation a primary circuit conducts pressurized fluid from the pressurized fluid source to one chamber of the appropriate one of the cylinders and a fluid reservoir receives fluid back from one chamber of the other cylinder.
In response to pressurized fluid entering and leaving the cylinder chambers communicating with the pressurized fluid source, a secondary circuit acts as a slave circuit merely shifting fluid back and forth between the cylinder chambers which are not communicating with the pressurized fluid source.
Should there be a rupture in a portion of the circuit conducting pressurized fluid between the pressurized fluid source and either of the cylinders, that circuit portion and the associated cylinder are automatically cut out of the circuit and the pressurized fluid normally conducted through that portion is diverted to the slave circuit and passes to the chamber of the other cylinder communicating with that slave circuit.